Is the project still alive and maintained ?
I would be glad to send some pull requests to fix bugs, but there isn't any new version since June 2015 and no activity from @greatman since June 2016.
If someone is interested : https://github.com/Aztorius/craftconomy3

I was also trying to use this plugin as it stated support for sponge but I encountered this error. Is sponge still supported? Is this project still alive?

[12:01:04 ERROR] [Sponge]: Skipping plugin with invalid plugin ID 'GreatmancodeToolsLoader' from mods\craftconomy3-3.3.jar. Plugin IDs should be lowercase, and only contain characters from a-z, dashes or underscores, start with a lowercase letter, and not exceed 64 characters.